標題: A question about friction [打印本頁] 作者: abc666 時間: 21/4/2008 06:55 PM 標題: A question about friction Explain why the coefficient of kinetic friction is smaller than that of static friction.
AL PHY TAS A1 Q.3
上堂好像講過,但忘記了=.=作者: sapphire 時間: 22/4/2008 08:42 PM consider a moving block on a rough plane
let: N be the normal reaction of the block F be the force acting on it f be the frictional force acting on it mg be the weight of the block R be the reaction of the block when moving
static friction f = (μ1)N
when the block is moving, R is the force that need to balance the resultant force of F and mg so that R is not a vertical force in fact, R = Ncosθ (the value of cosθ is refered to the vector sum of F and mg, but it is always less than 1) so that, R < N for all values of cosθ
kinetic friction f = (μ1)Ncosθ = (μ2)N where μ2 = (μ1)cosθ
as a result, kinetic friction is always less than static friction